The objectives of the proposed project are: 1. to continue development of the necessary instrumentation and techniques to utilize electron energy loss spectroscopy as an important complement to X-ray spectroscopy for the elemental microanalysis of biological material. Then, through this development, to utilize the increased sensitivity of the energy loss technique (particularly for low Z biological materials) to detect smaller elemental concentrations and/or to obtain higher spatial resolution in the microanalysis of biological material than would be possible with x-ray techniques alone. (2) To apply the electron energy loss microanalysis technique to the specific problem of the subcellular localization of the major ions playing a role in excitation and contraction in myocardial cells. (In collaboration with J.B. Bassingthwaighte, T.E. Hutchinson, an A.P. MacKenzie who will be applying X-ray microanalysis techniques to this problem.) The proposed research should provide important information concerning myocardial cation distributions and also assess the usefulness and limitations of the energy loss microanalysis technique. It should thus serve as a guide for future investigations using energy loss microanalysis in both normal and diseased tissue.